YouTube Also Will Reserve Space for Advertisers That Commit to Buying in Top Shows

Google Inc. is ramping up its assault on traditional television's advertising business.

In a renewed effort to lure a bigger share of the advertising dollars that now flow to major TV networks, Google's YouTube is making a number of concessions long sought by marketers, ad executives say.

Most prominently, in discussions ahead of this spring's TV ad-selling season, YouTube has told marketers it will offer audience guarantees...